In electrosurgery, an electric scalpel is used to provide for cauterization as it cuts. The voltages that are generated by the electric scalpel may result in fibrillation if the pacer loop causes demodulation of the waveform. German standard DIN VDE 0750 Part 9 provides a test to determine if the pacer has suitable electrosurgery protection, i.e., a determination is made as to whether the pacer loop caused demodulation. The German standard requires that with a 500 kilohertz waveform that is 100 percent modulated at 50 hertz with 10 volts (20 volts peak to peak), applied to a series detection network (an ES demodulation detector) in the pacing loop, there would be no demodulation of the 50 hertz waveform.
In the prior art, back to back zener diodes have been used as the electrosurgery protection circuit. In one prior art embodiment the zener diodes that are used have a 9.1 voltage drop in the reverse direction and a 1 volt breakdown voltage in the forward direction. Therefore, the back to back diodes effectively have a 10.1 volt breakdown voltage in both directions. That breakdown voltage just exceeds the 10 volts of the German standard test waveform. Thus there will be no conduction in the diodes resulting in no demodulation.
However, while the back to back diodes are satisfactory for preventing the demodulation under the German Standard test, they are not satisfactory for protecting against defibrillation potentials. The defibrillation potentials are as high as 400 joules and would be applied typically by paramedics or physicians in the event that the patient went into fibrillation. Thus the back to back diodes do not protect against the defibrillation potentials because such defibrillation potentials may cause undesirable current flows within the pacer circuit and undesirable biasing of various elements of the pacer circuit. The defibrillation potential may cause a breakdown of the zener diodes resulting in 10 volts being applied across the tip and ring. The 10 volts that is applied across the tip and ring may cause current flows and improper biasing of some of the circuit elements as just discussed.
It is an object of the present invention to provide a circuit that prevents demodulation and also protects against the defibrillation voltages.
Another object of the present invention is to provide a protection circuit that is simple in construction and efficient to manufacture.
Other objects and advantages of the invention will become apparent as the description proceeds.